Revert "Revert "adb: add support for O_CLOEXEC to unique_fd pipe wrapper.""

Implement pipe2 ourselves on darwin.

This reverts commit 8d7069e0e467b5fc5a060a5677ca1749d4e0f01d.

Test: none!
Change-Id: I42c2a8d07712fe4ac75b5824f754e79a5b9f5cb4
1 file changed